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| Red algae | ||||||
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| Scientific classification | ||||||
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| Possible classes | ||||||
The red algae (Rhodophyta, IPA: /ˌroʊdəˈfaɪtə, roʊˈdɒfɨtə/, from Greek: ῥόδον (rhodon) = rose + φυτόν (phyton) = plant, thus red plant) are a large group, about 5,000–6,000 species D. Thomas (2002). Seaweeds. Life Series. Natural History Museum, London. ISBN 0-565-09175-1. of mostly multicellular, marine algae, including many notable seaweeds. Other references indicate 10,000 species. W. J. Woelkerling (1990). "An introduction", in K. M. Cole & R. G. Sheath: Biology of the Red Algae. Cambridge University Press, Cambridge, 1–6. ISBN 0-521-34301-1. Most of the coralline algae, which secrete calcium carbonate and play a major role in building coral reefs, belong here. Red algae such as dulse (Palmaria palmata) and laver (nori/gim) are a traditional part of European and Asian cuisine and are used to make other products like agar, carrageenans and other food additives. M. D. Guiry. Rhodophyta: red algae. Retrieved on 2007-06-28.
A red alga in a California tide pool displaying some iridescence when not covered with water
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The oldest fossil identified as a red alga is also the oldest fossil eukaryote that belongs to a specific modern taxon. Bangiomorpha pubescens, a multicellular fossil from arctic Canada, strongly resembles the modern red alga Bangia despite occurring in rocks dating to 1200 million years ago. N. J. Butterfield (2000). Bangiomorpha pubescens n. gen., n. sp.: implications for the evolution of sex, multicellularity, and the Mesoproterozoic/Neoproterozoic radiation of eukaryotes. Paleobiology 26 (3): 386–404.
Red algae are important builders of limestone reefs. The earliest such coralline algae, the solenopores, are known from the Cambrian Period. Other algae of different origins filled a similar role in the late Paleozoic, and in more recent reefs.
The red algae are classified in the Archaeplastida, along with the glaucophytes and Viridiplantae (green algae and land plants).
Below are two valid published taxonomies of the red algae, although neither necessarily has to be used, as the taxonomy of the algae is still in a state of flux (with classification above the level of order having received little scientific attention for most of the 20th century).G. W. Saunders & M. H. Hommersand (2004). Assessing red algal supraordinal diversity and taxonomy in the context of contemporary systematic data. American Journal of Botany 91: 1494–1507. If one defines the kingdom Plantae to mean the Archaeplastida, the red algae will be part of that kingdom; but if Plantae are defined more narrowly, to be the Viridiplantae, then the red algae might be considered their own kingdom or part of the kingdom Protista. The two classification systems below place the red algae in the plant kingdom.
There are around 6,500 to 10,000 known species, nearly all of which are marine, with about 200 that only live in fresh water. However estimates of the number of real species vary by 100%.
Some examples of species and genera of red algae are:
Pit connections and pit plugs are unique and distinctive features of red algae that form during the process of cytokinesis following mitosis. In red algae, cytokinesis is incomplete. Typically, a small pore is left in the middle of the newly formed partition. The pit connection is formed where the daughter cells remain in contact.
Shortly after the pit connection is formed cytoplasmic continuity is blocked by the generation of a pit plug, which is deposited in the wall gap that connects the cells.
Connections between cells having a common parent cell are called a primary pit connections. Because apical growth is the norm in red algae, most cells have two primary pit connections, one to each adjacent cell.
Connections that exist between cells not sharing a common parent cells are labeled secondary pit connections. These connections are formed when an unequal cell division produced a nucleated daughter cell that then fuses to an adjacent cell. Patterns of secondary pit connections can be seen in the order Ceramiales.
After a pit connection is formed, tubular membranes appear. A granular protein, called the plug core, then forms around the membranes. The tubular membranes eventually disappear. While some orders of red algae simply have a plug core, others have an associated membrane at each side of the protein mass, called cap membranes. The pit plug continues to exist between the cells until one of the cells dies. When this happens, the living cell produce a layer of wall material that seals off the plug.
It is thought that the pit connections function as structural reinforcement, and as an avenue for cell to cell communication and/or symplastic transport in red algae.[citation needed] While the presence of the cap membrane could inhibit this transport between cells, it has been hypothesized that the tubular plug cores serve as a means of transport.
Several species are used as food. Dulse (Palmaria palmata)Dulse: Palmaria palmata. Quality Sea Veg. Retrieved on 2007-06-28. and Porphyra are the best known in the British Isles. T. F. Mumford & A. Muira (1988). "Porphyra as food: cultivation and economics", in C. A. Lembi & J. Waaland: Algae and Human Affairs. Cambridge University Press, Cambridge. ISBN 0-521-32115-8.
In East and Southeast Asia, agar is most commonly produced from Gelidium amansii.
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